A 245-YEAR NAO RECORD FROM OCEAN QUAHOGS (BIVALVIA, NE ATLANTIC, NORTH SEA)

Existing reconstructions of the winter North Atlantic Oscillation (wNAO) are based on terrestrial proxies and historical documents. No direct high-resolution, long-term records from marine settings are available for this major climate-dictating phenomenon, which severely affects a variety of economic aspects of our society. Here we present a 245-year proxy wNAO index based on shells of the long-lived marine bivalve mollusk, Arctica islandica. Variations in annual (annual periodicity confirmed by oxygen isotope record of the shells) rates of shell growth are positively correlated with wNAO-related changes in the food supply. Maximum amplitudes in frequency bands of 7 to 9 and 5 to 7 years fall exactly within the range of instrumental and other proxy wNAO indices. These estimates were obtained for specimens live-collected 2000km apart, in the Central North Sea and the Norwegian Shelf. Hence, the wNAO influences hydrographic regimes of large regions of the ocean. Our study demonstrates that A. islandica can reliably reconstruct wNAO dynamics for time intervals and regions without instrumental measurements. Our new tool functions as a unique, independent proxy for the wNAO index prior to the 20th century greenhouse forcing and has the potential to further validate other proxy-based wNAO records.